The invention relates to subsidence hydraulic dredging which provides an environmentally superior procedure, allowing deepening of bodies of water and shoreline regions without destroying shell-fish and removing surface sediments contained therein. In particular, subsidence dredging provides a method whereby the deeper sand layers under a body of water and coastal waters, particularly shoreline regions, can be winnowed and added to beach regions as "beach nourishment" thereby avoiding costly barging of silt sediments to approved disposal sites.
Applicant is aware of other prior art dredging procedures. One such procedure is disclosed in U.S. Pat. No. 3,645,018 to Dekoning et al., which discloses a suction pipe inserted into a layer of sand by way of a layer of clay, and a layer of water. Another prior art device is disclosed in U.S. Pat. No. 4,296,970 to Hodges, which discloses a hydraulic mining apparatus for operation in tar-like sand formation with a cutting jet nozzle. A further prior art device is disclosed by U.S. Pat. No. 3,645,018, to DeKonig et al., which discloses a method of measuring pressures in sand surrounding a suction pipe, the sand being covered by a layer of silt, wherein the sand may be dredged to the exclusion of the silt. DeKonig et al. is directed toward measuring the differences in specific gravities of the sand and the silt and for moving the lower end of the suction pipe so as to maintain it below the silt at all times during the suction dredging operation. While the above prior art devices show use of hydraulic mining apparatus having a cutting jet nozzle and the use of a suction pipe inserted into a layer of sand for underwater dredging, such prior art does not comprise the jetting and intake suction arrangements with screening for beach sand as it is employed in the Applicant's subsidence dredging method. Neither does the prior art show an associated seismic arrangement for determination of the extent of the mined cavity. Therefore the prior art is distinguishable. Furthermore, the prior art does not suggest the inventive combination of subsurface mining using a jetting intake for removing sand for glacial out wash deposits in combination with seismic devices to determine the extent of the subsidence dredging.
Accordingly, it is desirable to provide for a new and improved apparatus and method for subsidence dredging including hydraulic jetting and suction combined with hydraulic winnowing action for producing quality beach sand to provide an environmentally superior procedure for deepening shoreline regions without destroying shellfish and for replenishment/nourishment of the adjacent beach areas, which overcomes at least some of the disadvantages of the prior art.